JP2013050385A - Power measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power measuring instrument that allows all current transformers of a plurality of kinds different in output to be connected to a current detecting part, without requiring time and effort for switching circuits in the power measuring instrument, and thereby enables power of a circuit in a power distribution board to be measured.SOLUTION: A power measuring instrument 3 comprises: a current detecting part 31 for detecting current signals on the basis of output from current transformers 2a and 2b; a voltage detecting part 32 for detecting voltage signals; and a power calculating part 33 for calculating power on the basis of all the voltage and current signals detected with the voltage detecting part 32 and the current detecting part 31. In the current detecting part 31, load resistors 311a and 311b are connected in series. The current transformers 2a and 2b comprise two different kinds different in output, and are connected, according to the respective kinds, to both ends of the load resistors 311a and 311b connected in series or to connection terminals 3a-3c between the load resistors 311a and 311b. According to this configuration, the power measuring instrument 3 allows the current transformer 2a or 2b to be connected to the current detecting part 31, and thereby measures the power of a circuit in a power distribution board.

Description

  The present invention relates to a power measuring instrument that is connected to a current transformer (CT) and measures the power of a circuit in a distribution board or the like.

  Conventionally, when measuring the power of a circuit in a distribution board provided in a facility such as a building, a current transformer is used to expand the measurement range. A power meter is connected to the receiving circuit of this current transformer, and the power meter inserts a burden resistor into the circuit connected to the current transformer, and detects the voltage across this burden resistor. Electric power calculation can be performed by measuring the current value.

  In factories and the like, an alternating current of 100 A to several hundreds of A is energized, and a current transformer called a pair 5A (hereinafter referred to as a pair 5ACT) that can obtain an output current of 5 A when a rated current is passed is used. This pair 5ACT is a so-called standardized output method when current measurement of the distribution system is performed, and a flexible power measurement system can be configured by combining with a connectable power meter.

  In the past, most of the power measurement of circuits in the distribution panel has been to measure only the main circuit through which a large current flows. However, in order to realize “visualization” of power consumption in recent years, it is branched from the main circuit. It is also necessary to measure the power of the branch circuit which is the terminal circuit in the distribution board. Since the current from the main circuit is divided into this branch circuit, for example, a current of about several tens of A flows. In the “visualization” of power, information on the power for each circuit in the distribution board is displayed on a management device equipped with a monitor via the LAN.

  And since said pair 5ACT outputs 5A at the time of energization of the rated current of several hundred A, it is necessary to enlarge a core, and a shape becomes comparatively large. Therefore, in a current measurement of about several tens of A in a branch circuit with a low rated current, when it is attempted to attach a pair 5ACT to a measurement location where current is applied, the shape is large and cannot be attached. In addition, there is a problem in terms of space in the distribution board that all power measurements of a plurality of branch circuits in the distribution board are performed with 5 ACT.

  For this reason, in the current measurement of the branch circuit, a small current transformer (hereinafter referred to as a small CT) having an output current of about several tens of mA is used instead of 5 ACT. Since the output current of this small CT is one-hundredth of that of 5ACT, the iron core and the winding can be downsized. Therefore, the compact CT can be used for current measurement of a branch circuit or the like having a relatively low current in the distribution board at a location that cannot be used in the case of the pair 5ACT due to shape restrictions. Thus, it is necessary to use different types of current transformers according to the installation space in the distribution board.

  Next, the burden resistance connected to the current transformer and provided in the power meter will be described with reference to FIG. As shown in FIG. 15A, since the small CT 151 has an output current of several mA, the burden resistor 154 provided in the current detector 153 of the power measuring instrument 152 as a receiving circuit has a resistance value of several Ω. Is used. The current detection unit 153 measures the current value by detecting the voltage across the burden resistor 154 and outputs the current value to the power calculation unit 155. On the other hand, as shown in FIG. 15 (b), the output current of the pair 5ACT156 is 5A at the maximum, so it is connected to a shunt resistor 157 of several mΩ, and the current detection unit 153 detects the voltage across the shunt resistor 157. Thus, the current value is measured and output to the power calculation unit 155.

  By the way, a current transformer is disclosed that is easy to assemble, requires a small installation area, has high measurement accuracy, and can be easily adapted even when the detected current is different (see, for example, Patent Document 1).

JP-A-7-229927

  As described above, different types of current transformers such as the small CT and the pair 5 ACT have different output currents, so that the resistance values of the burden resistors of the connected circuits are different. Specifically, as shown in FIG. 15, there is a difference of about 1000 times in output current between the small CT 151 and the pair 5 ACT 156, and the burden resistance connected to the pair 5 ACT 156 is several mΩ and is connected to the small CT 151. The burden resistance is several Ω. For this reason, in order to measure the power of the circuit using different types of current transformers, according to the type of current transformer, separate measurement circuit units that divide the input terminal by the size of each output current, Alternatively, there is a problem that a separate power meter is required and costs are increased.

  Further, in the case where the power measuring device is connectable to both the pair 5ACT and the small CT, a circuit switcher (multiplexer) for switching the output signal between the pair 5ACT and the small CT is required, which requires cost.

  Furthermore, in the said patent document 1, the current measurement from which a magnitude | size differs is implement | achieved by using one type of current transformers and switching a resistor, and electric power is measured using different types of current transformers. It is not a thing.

  The present invention has been made in view of the above problems, and does not require the trouble of switching the circuit in the power meter, and allows any of a plurality of types of current transformers having different outputs to be connected to the current detection unit. An object of the present invention is to provide a power meter capable of measuring the power of a circuit in a distribution board or the like.

  In order to achieve the above object, the present invention provides a voltage detection unit that detects a voltage signal from a circuit, a current detection unit that detects a current signal based on an output from a current transformer attached to the circuit, A power calculation unit that calculates power based on voltage and current signals detected by the voltage detection unit and the current detection unit, wherein the current detection unit includes at least two types of burden resistances. A signal processing circuit connected in series and processing the voltage of the burden resistor connected in series, wherein the current transformer is composed of at least two kinds of different outputs, and these current transformers are Depending on the type, the load resistor connected in series is connected to a predetermined position or another predetermined position different from the predetermined position.

  In this power meter, a conduction relay is connected in parallel to at least one of the burden resistors connected in series, and the current transformer is the most of the burden resistor connected in series. It is preferable to be connected to both ends.

  In this power meter, the current detection unit is connected to a predetermined position at an end of the burden resistor, and a common connection terminal to which a signal line serving as a reference of the output of the current transformer is connected, and the burden resistor Circuit switching for selecting an individual connection terminal to which the other signal line of the current transformer is connected to a predetermined position of an end of the current transformer and a path of the signal line connected to the power calculation unit from the individual connection terminal It is preferable to further include a multiplexer having a function.

  In this power meter, the power calculation unit includes a signal detection unit that detects the magnitude of a current signal input from the current detection unit, and the signal detection unit is based on the magnitude of the current signal. Thus, it is preferable to switch the setting of the relay or the multiplexer to another circuit.

  In this power measuring instrument, it is preferable that the order of connecting the plurality of burden resistors in series lowers the resistance value of the burden resistor on the reference potential side.

  In this power meter, it is preferable that the signal line on the reference potential side connected to the burden resistor is connected to a predetermined reference potential other than 0 V which is the ground.

  In the power measuring instrument, it is preferable that the current detection unit further includes a programmable gain amplifier capable of changing a signal amplification factor.

  In this power measuring instrument, it is preferable that the connection terminal provided between the burden resistors is provided individually for each type of current transformer, not shared by different types of current transformers.

  In this power measuring instrument, the connection terminal connected to the burden resistor having a larger resistance value among the at least two types of burden resistors connected in series has a structure in which only a dedicated terminal can be connected. Is preferred.

  In this power meter, the signal line from the current transformer is preferably connected to a connector terminal having a shape that fits with the connection terminal.

  In this power meter, the connector terminal preferably has a structure to which at least two signal lines from the current transformers can be connected.

  In this power meter, the circuit includes a main circuit and a plurality of branch circuits branched from the main circuit, and the connection terminals are arranged adjacent to each other on the side surface of the power meter. Is preferred.

  In this power meter, the connection terminal includes a screw terminal for connecting a signal line of the current transformer having a large output, and a connector terminal for connecting a signal line of the current transformer having a small output, and the current transformer The plug connected to the signal line preferably has a structure that covers the other connection terminal when connected to one of the screw terminal or the connector terminal.

  In this power meter, it is preferable that multi-circuit power measurement is possible.

  In this power measuring instrument, it is preferable that the connection terminal is configured to include only the screw terminal or only the connector terminal for some of the multiple circuits.

  The present invention also provides a voltage detection unit that detects a voltage signal from a circuit, a current detection unit that detects a current signal based on an output from a current transformer attached to the circuit, the voltage detection unit, And a power measuring unit that calculates power based on each signal of voltage and current detected by the current detecting unit, wherein the current detecting unit includes at least two types of burden resistors arranged in parallel. A circuit switch that is connected to one end side of the load resistor arranged in parallel and switches the current path of the output of the current transformer to any one of the load resistors connected in parallel; and the current detection unit And a control circuit unit for controlling the circuit switch based on the magnitude of the current detected in step (a), and the current transformer is composed of at least two types of outputs different from each other. Parallel It is connected to both ends of the connected load resistance, characterized in that.

  The power measuring instrument according to the present invention includes a current detection unit in which at least two types of burden resistors are connected in series, and the current transformer has a predetermined burden resistor connected in series according to the type. It may be connected to a position or another predetermined position different from the predetermined position. Therefore, different types of current transformers can be connected to the same power meter, and the power of the circuit in the distribution board can be measured.

1 is an overall configuration diagram of a power measurement system including a power meter according to Embodiment 1 of the present invention. It is a functional block diagram of the power meter. It is a circuit diagram of the electric current detection part with which the said electric power measuring device is equipped. It is a circuit diagram of the electric current detection part with which the electric power meter which concerns on the modification 1 of the said Embodiment 1 is equipped. It is a circuit diagram of the electric current detection part with which the electric power meter which concerns on the modification 2 of the said Embodiment 1 is equipped. It is a circuit diagram of the electric current detection part with which the electric power measuring device which concerns on the modification 3 of the said Embodiment 1 is equipped. It is a circuit diagram of the electric current detection part with which the electric power meter which concerns on the modification 4 of the said Embodiment 1 is equipped. It is a circuit diagram of the electric current detection part with which the electric power meter which concerns on Embodiment 2 of this invention is equipped. It is a circuit diagram of the electric current detection part with which the electric power measuring device which concerns on Embodiment 3 of this invention is equipped. It is a circuit diagram of the electric current detection part with which the electric power meter which concerns on the modification 1 of the said Embodiment 3 is equipped. It is a circuit diagram of the electric current detection part with which the electric power meter which concerns on the modification 2 of the said Embodiment 3 is equipped. (A) The front view of the electric power meter which concerns on Embodiment 4 of this invention, (b) The bottom view of the electric power meter, (c) The top view of the electric power meter. (A) The side view of the plug of the current transformer connected to the electric power meter which concerns on the modification 1 of the said Embodiment 4, (b) The perspective view of the plug, (c) With another side view of the plug is there. (A) The front view of the electric power measuring device which concerns on the modification 2 of the said Embodiment 4, (b) The bottom view of the same electric power measuring device, (c) The top view of the same electric power measuring device. (A) Circuit diagram of current detector in conventional power meter, (b) Circuit diagram of current detector in another conventional power meter.

(Embodiment 1)
A power meter according to Embodiment 1 of the present invention will be described with reference to the drawings. As shown in FIG. 1, the power measurement system S includes a distribution board 1, different types of current transformers 2 a and 2 b, a power meter 3, a monitoring device 4, a load 5, and breakers 6 a, 6 b and 6 c. The power measurement system S monitors the power consumption of various loads 5 such as a lighting fixture or a personal computer that receives power supply from the distribution board 1 in an office building or a general house, for example.

  The distribution board 1 includes a main circuit that receives commercial power supplied from outside to the building or house on the primary side via the electric wires 7, and a plurality of electric circuits that are installed on the electric circuit branched from the secondary side of the main circuit. And a branch circuit. Each branch circuit is connected to various loads 5 such as an air conditioner and an IH device in addition to a lighting fixture and a personal computer. Moreover, the breaker 6a is a main breaker connected to the electric wire 7 of the main circuit, and the breaker 6b is a branch breaker disposed in a plurality of branch circuits branched from the main circuit.

  Different types of current transformers 2a and 2b reduce the current of each circuit at a constant rate and supply it to the power meter 3 via the signal line 8 which is a dedicated cable. For example, if the current transformer 2a is a 400 / 5A type penetration type, the number of turns of the coil is configured so that when a current of 400A flows through the electric wire 7 passing through the center portion, 5A flows through the signal line 8 on the output side. ing.

  The current transformer 2a is installed in order to periodically measure the main current flowing through the main circuit through which a relatively large current flows. In this figure, the electric current measuring device 2a is penetrated by two electric wires of the main circuit wiring. 3 and signal line 8. The current transformer 2b is installed in order to periodically measure the branch current flowing through each branch circuit through which a relatively small current flows for each branch circuit, and is passed through a predetermined position of the electric wire of the branch circuit. Connected by signal line 8. The current transformers 2a and 2b can be easily attached to the main circuit 7 and the branch circuit wires 7 by a split type or the like, and by using a dedicated cable as the signal line 8, erroneous connection can be prevented.

  The power measuring instrument 3 is connected to the current transformers 2a and 2b, and has a burden resistor to be inserted into a circuit connected to the current transformers 2a and 2b. The power measuring instrument 3 supplies the power of the circuit in which the current transformers 2a and 2b are installed. measure. The power meter 3 outputs the calculation result to the monitoring device 4 via the communication line. The power measuring instrument 3 has a size of 10 × 10 cm, for example, and is installed at a predetermined location in the distribution board 1.

  The monitoring device 4 is a dedicated personal computer or the like having a monitor, and is a monitoring unit that manages and displays energization information of each branch circuit. The monitoring device 4 is connected to the power meter 3 via RS-485 communication or the like, collects data related to the power usage of each load 5, and displays a graph or the like for data analysis. The monitoring device 4 automatically records, for example, data relating to power usage every hour or every day, performs collective energy management via a network connected to the power meter 3, and “visible” the efficient power usage is seen. Realization.

  The load 5 is various electric devices such as an air conditioner and an IH device, in addition to a lighting device and a personal computer connected to the branch circuit.

  Next, the functional configuration of the power meter 3 according to the first embodiment will be described with reference to FIG. The power meter 3 includes a current detector 31 that detects a current from signals from the current transformers 2a and 2b, a voltage detector 32 that detects a voltage signal of the circuit, and a current and voltage detector 32 in the current detector 31. A power calculation unit 33 that calculates power based on each voltage signal is provided.

  The current detection unit 31 adds a predetermined value to the load resistor 311 inserted in a circuit connected to the current transformers 2a and 2b, a filter 312 that passes a signal in a predetermined frequency band, and a current signal that has passed through the filter 312. An adder circuit 313 is provided.

  The voltage detector 32 is connected to the electric wire 7 via a breaker 6c shown in FIG. 1 and the like, and includes a voltage step-down circuit 321, a filter 322, and an adder circuit 323. The voltage step-down circuit 321 steps down the voltage, the filter 322 passes a voltage signal in a predetermined frequency band, and the addition circuit 323 applies an appropriate bias to the voltage signal so that the voltage waveform falls within a range of, for example, 0 to 5V. Call.

  Based on the current measured by the current detector 31 and the voltage detected by the voltage detector 32, the power calculator 33 supplies the load 5 connected to the electric wire 7 to which the current transformers 2a and 2b are attached. It is a microcomputer that calculates the electric power. The power calculation unit 33 includes A / D conversion units 331 and 332, a multiplication unit 333, and a transmission circuit unit 334.

  The A / D converter 331 converts the analog signal received from the voltage detector 32 into a digital signal. The A / D converter 332 converts the analog signal received from the current detector 31 into a digital signal. The multiplier 333 is a circuit that multiplies the signals output from the A / D converters 331 and 332, that is, calculates power. The transmission circuit unit 334 includes, for example, a two-wire serial communication circuit compliant with RS485 and transmits a power calculation value to the monitoring device 4 that can communicate with each other via a connected communication line.

  Next, the circuit configuration of the current detection unit 31 provided in the power meter 3 according to the first embodiment will be described with reference to FIG. The current detection unit 31 includes two types of burden resistors 311a and 311b connected in series and having different resistance values. For example, the burden resistor 311a is a 2.0Ω resistor, and the burden resistor 311b is a 1 mΩ shunt resistor. Note that the shunt resistor is a highly accurate resistor with a small resistance value made for current measurement of a circuit through which a large current flows.

  Further, the signal line on the reference potential side connected to the burden resistors 311a and 311b is connected to the 0V ground (GND) 314, and one end of the burden resistor 311a is connected to the adder circuit 313 side. As described above, the current detection unit 31 includes a signal processing circuit that measures the voltages at both ends of the load resistors 311a and 311b inserted in the circuit and obtains a current value.

  The power measuring instrument 3 includes connection terminals 3a to 3c that are connected to the ends of the load resistors 311a and 311b, respectively. The current transformers 2a and 2b have two different outputs as described above, and the current transformers 2a and 2b are arranged at the extreme ends of the load resistors 311a and 311b connected in series according to the type. Or it connects to the predetermined position between burden resistance 311a, 311b.

  That is, the signal line from the pair 5ACT 2a that outputs a relatively large current is connected to the connection terminals 3b and 3c because it is necessary to reduce the burden resistance inserted in the circuit. On the other hand, since the signal line from the small CT 2b that outputs a relatively small current needs to increase the resistance value of the burden resistance inserted in the circuit connected to the current transformers 2a and 2b, the connection terminals 3a and 3c Connected to. As described above, the connection terminal 3c is a common terminal for connecting the signal lines serving as the reference of the outputs of the current transformers 2a and 2b, and the connection terminal 3a is an individual terminal for connecting other signal lines of the current transformer 2b. The connection terminal 3b is an individual terminal for connecting the other signal line of the current transformer 2a.

  As described above, in the power measuring instrument 3 according to the first embodiment, the connection positions of the signal lines of the different types of current transformers 2a and 2b are set according to the resistance values of the load resistors 311a and 311b connected in series. It can adjust by changing the connection terminals 3a-3c provided. For this reason, in the electric power measuring device 3, the effort which switches a circuit is not required, the current transformers 2a and 2b from which an output differs can be connected to the same electric current detection part 31, and the electric power of the circuit in the distribution board 1 is made. The current measuring device 3 can be reduced in size and cost.

  Conventionally, when a current transformer 2 with different outputs is connected to a single power meter 3, a circuit switch (multiplexer) or the like is required. However, a current transformer 2 with different outputs is used. Thus, it is possible to measure power with a single power meter 3 that does not require a circuit switch or the like. Furthermore, the monitoring device 4 connected to the power meter 3 can “visualize” the power consumption of the load 5 and visually understand which load 5 the power should be reduced. Energy saving can be realized.

  As shown in FIG. 3, the order of connecting the plurality of burden resistors 311a and 311b in series lowers the resistance value of the burden resistor 311b on the reference potential 314 side. Thereby, a voltage drop can be suppressed low with respect to the reference potential 314, the circuit of the power meter 3 can be stably operated, and the influence of noise and the like can be reduced.

(First modification)
A first modification of the first embodiment will be described with reference to FIG. In the present modification, in the current detection unit 31, among the load resistors 311a and 311b connected in series, a conduction relay 315 is connected in parallel to the load resistor 311a. The connection terminals 3a and 3c are respectively connected to the extreme ends of the load resistors 311a and 311b connected in series, and the current transformers 2a and 2b having different outputs are connected to the same connection terminals 3a and 3c. In this modification, unlike the first embodiment, among the load resistors 311a and 311b connected in series, a load resistor 311a having a large resistance value is arranged on the reference potential 314 side.

  Next, the operation of the power meter 3 according to this modification will be described. When the pair 5ACT2a is connected to the connection terminals 3a and 3c, the relay 315 is manually controlled to be in a closed state, and the output current from the pair 5ACT2a passes only through the shunt resistor 311b. On the other hand, when the small CT 2b is connected to the connection terminals 3a and 3c, the relay 315 is manually controlled to be in an open state, and the output current from the small CT 2b passes through the shunt resistor 311b and the burden resistor 311a. For this reason, in the power meter 3 according to this modification, the current transformers 2a and 2b having different outputs can be connected to the same current detection unit 31 with a low-cost configuration using the relay 315 having the 1a contact configuration. To do.

  The power calculation unit 33 includes a signal detection unit 335 that detects the magnitude of the current signal input from the current detection unit 31, and the signal detection unit 335 includes the magnitude of the current input from the current detection unit 31. Based on this, it is conceivable to automatically control the open / closed state of the relay 315. In this case, for example, in a state where the pair 5ACT 2a is connected, it is possible to appropriately prevent the burden resistance 311a from being burned out due to the state (open state) of the relay 315 matched to the small CT 2b.

(Second modification)
A second modification of the first embodiment will be described with reference to FIG. In the second modification, the current detection unit 31 is connected to a predetermined position at the ends of two types of burden resistors 311a and 311b connected in series, and a signal line path that connects the connection terminals 3a to 3c to the power calculation unit 33. It further includes a multiplexer 316 having a circuit switching function for selecting. The multiplexer 316 performs automatic switching according to the set value based on the signal input from the power calculation unit 33. For this reason, in the power meter 3 according to the second modification, a signal multiplexer 316 having a low current capacity is used as a circuit switch, and the current transformers 2a and 2b having different outputs are connected to the same current detector 31. The power of the circuit in the distribution board can be measured as possible. Therefore, it is possible to reduce the size and cost of the power measuring instrument 3.

(Third Modification)
A third modification of the first embodiment will be described with reference to FIG. In the third modification, in addition to the configuration of the second modification, the current detection unit 31 further includes a programmable gain amplifier 317 capable of changing a signal amplification factor. The programmable gain amplifier 317 is an amplifier circuit that can set the amplification factor from the outside using an analog switch or the like. The outputs of the current transformers 2a and 2b differ depending on the rated current. However, in the power measuring instrument 3 according to the third modification, the gain is switched using the programmable gain amplifier 317, and a signal is input to the adder circuit 313 with an optimum signal. The power calculation unit 33 can calculate the power.

(Fourth modification)
A fourth modification of the first embodiment will be described with reference to FIG. In the fourth modification, the signal line on the reference potential side connected to the burden resistors 311a and 311b is connected to a predetermined reference potential Vref other than 0V that is the ground. With this configuration, when a signal is input to the AD conversion unit 332 of the power calculation unit 33, the reference potential Vref can be applied, the configuration of the adder circuit 313 for the signals obtained by the burden resistors 311a and 311b is unnecessary, and the signal line is directly connected. The AD converter 332 of the power calculator 33 can be connected. Therefore, in this modification, the circuit configuration of the current detection unit 31 is simplified to reduce the cost, and the current transformers 2a and 2b having different outputs can be connected to the same current detection unit 31. The power of the circuit can be measured. Further, the power meter 3 can be reduced in size and cost.

(Embodiment 2)
A power meter according to Embodiment 2 of the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the structure similar to the said Embodiment 1, and the detailed description is abbreviate | omitted (hereinafter the same).

  The current detection unit 31 includes a circuit switcher (1c) having a circuit configuration in which two load resistors 311a and 311b arranged in parallel and the current path of the outputs of the current transformers 2a and 2b are any one of the load resistors 311a and 311b. A relay having a contact configuration) 318 and an adder circuit 313. The power calculation unit 33 includes a control circuit unit 336 that controls the circuit switch 318 based on the magnitude of the current detected by the current detection unit 31. One of the signal lines of the current transformers 2a and 2b is connected to the connection terminals 3a and 3c connected to both ends of the load resistors 311a and 311b connected in parallel, regardless of the type.

  For this reason, in this Embodiment 2, even if any of current transformer 2a, 2b is connected to the electric power measuring device 3, the appropriate load resistance according to the kind of current transformer 2a, 2b by the circuit switch 318 is shown. 311a and 311b can be connected. Therefore, the signal level of the current detection signal is raised to a predetermined level, the S / N ratio is improved, and the power can be accurately measured.

(Embodiment 3)
A power meter according to Embodiment 3 of the present invention will be described with reference to FIG. In the third embodiment, the connection terminals 3b and 3d provided between the load resistors 311a and 311b connected in series of the current detection unit 31 are not shared by the different types of current transformers 2a and 2b, and those types are not used. Each is provided separately. That is, as shown in FIG. 9, the connection terminals 3a and 3d are connected to the signal line of the small CT 2b, and the connection terminals 3b and 3c are connected to the signal line of the pair 5ACT 2a. With this configuration, the current transformers 2a and 2b having different outputs can be connected to the same current detection unit 31, the power of the circuit in the distribution board can be measured, and the current flow path from the current transformers 2a and 2b flows. Can be completely separated, and more accurate power measurement becomes possible.

(First modification)
A first modification of the third embodiment will be described with reference to FIG. In this modification, the connection terminals 3a and 3d connected to the burden resistor 311a having a larger resistance value cannot be connected except for a dedicated connector terminal (plug) 9a, that is, a connector shape that fits with the shape of the connector terminal 9a. 3e.

  With this configuration, in this modified example, the pair 5ACT 2a is connected to the burden resistor 311a having a large resistance value, and the burden resistor 311a is burned out, thereby preventing an accident due to erroneous connection. Moreover, the construction between the current transformers 2a and 2b and the power measuring device 3 can be improved by adopting the structure of the connector terminal 9a.

(Second modification)
A second modification of the third embodiment will be described with reference to FIG. In this modification, the connector terminal (plug) 9b has a structure to which signal lines from two or more current transformers (two small CTs 2b in this figure) can be connected. On the other hand, the power measuring instrument 3 is formed with a connector connection terminal 3f having a shape that fits with the connector terminal 9b on the side surface or the like. With this configuration, in addition to the effect of the first modification, a plurality of current transformers 2a and 2b attached to the R / S / T phase, such as power measurement from a wire using a three-phase three-wire system, are set. In the circuit measurement, it is possible to prevent erroneous connection.

(Embodiment 4)
A power meter according to Embodiment 4 of the present invention will be described with reference to FIG. The power meter 3 according to the fourth embodiment includes a display unit 10, a switch unit 11, a voltage input terminal 12, a communication terminal 13, a pair 5ACT connection terminal 14, and a small CT connection terminal 15.

  The display unit 10 is a liquid crystal panel or the like that displays a power measurement result in each circuit. The switch unit 11 is an operation key for setting the types of the current transformers 2 a and 2 b and setting the display of the display unit 10. The voltage input terminal 12 is an input terminal that is connected to an electric wire and detects a correlation voltage between the voltage electrode S and the voltage electrode T. The communication terminal 13 is a screw terminal that is connected to the monitoring device 4 and connects a communication line used for RS-485 communication or the like. The pair 5ACT connection terminal 14 is a screw terminal for connecting a signal line from the pair 5ACT2a. The small CT connection terminal 15 is a connector terminal serving as an insertion port into which the connector terminal 9a from the small CT 2b is inserted.

  And as shown in the area | region of the dotted line L, the connection terminals 14 and 15 are arrange | positioned at linear form in the up-down direction for every circuit which consists of a main circuit and several branch circuits branched from the said main circuit, and a different circuit Are arranged on the side surface of the power meter 3 adjacent to each other in the left-right direction. With this arrangement configuration, the power meter 3 according to the fourth embodiment can visually prevent a plurality of current transformers 2a and 2b from being connected to the same circuit at the same time.

(First modification)
A first modification of the fourth embodiment will be described with reference to FIG. As shown in FIG. 12, the power meter 3 includes a connection terminal 14 that is a screw terminal for connecting a signal line of a current transformer 2a having a large output, and a connector for connecting a signal line of a current transformer 2b having a small output. A connection terminal 15 as a terminal is provided. And in this modification, as shown to Fig.13 (a)-(c), when the connector terminal 16b is inserted in the connection terminal 15, the plug 16 connected to the signal wire | line of current transformer 2a, 2b is inserted. And a protrusion 16a covering the connection terminal 14 which is a screw terminal.

  With this configuration, two types of current transformers 2a and 2b are not simultaneously connected in the same circuit, and erroneous connection due to simultaneous connection of the small CT 2b and the pair 5ACT 2a can be prevented. In addition, it can also be considered that the structure of the plug 16 is a structure in which the connection terminal 15 that is a connector terminal cannot be connected when the connection terminal 14 that is a screw terminal is connected.

(Second modification)
A second modification of the fourth embodiment will be described with reference to FIG. In this modification, as shown by the area of the dotted line L2, the connection terminal of the power measuring instrument 3 has only the connection terminal 14 of the screw terminal in some circuits measured by the current transformers 2a and 2b. .

  This is because when the main circuit and the branch circuit in the distribution board are measured, the main circuit has a larger rated current, so it is 5 ACT2a, and the branch circuit has a relatively low rated current, so a small CT 2b is selected and measured. Therefore, in the power meter 3, since the predetermined circuit is a selection formula of only the connection terminal 14 of the 5ACT2a and the predetermined circuit is a selection formula of the connection terminal 15 of the small CT2b or the connection terminal 14 of the pair 5ACT2a, all the circuits are selective formulas. It can be configured at a lower cost than the structure of the connection terminals 14 and 15. Although not shown, it is also conceivable that a part of the measurement circuit has only the connection terminal 15 for the small CT 2b.

  The power measuring device 3 according to each of the above embodiments includes a plurality of connection terminal sets for measuring the power of a circuit composed of a main circuit and a branch circuit, and enables multi-circuit power measurement. This is because, when measuring from the main circuit to the branch circuit, it is necessary to measure a plurality of rated currents, and it is possible to reduce the size of the power measuring instrument 3 by enabling multi-circuit power measurement.

  The present invention is not limited to the configuration of the embodiment described above, and various modifications can be made without departing from the spirit of the invention. For example, the types of current transformers 2a and 2b and burden resistors 311a and 311b are not limited to two types, and may be at least two types. Moreover, the type of current transformer is not limited to 5 ACT or small CT, and current transformers with rated currents of 50A, 250A, 600A can be used. Furthermore, various types of different current transformers may be connected to a predetermined position of a plurality of burden resistors connected in series or another predetermined position different from the predetermined position, depending on the type. It is not limited to the positions at the extreme ends.

1 Distribution board 2a Current transformer (vs. 5ACT)
2b Current transformer (small CT)
DESCRIPTION OF SYMBOLS 3 Electric power measuring device 3a-3d Connection terminal 3e, 3f Connector connection terminal 4 Monitoring apparatus 5 Load 6a, 6b, 6c Breaker 7 Electric wire 8 Signal line 9a, 9b Connector terminal 10 Display part 11 Switch part 12 Voltage input terminal 13 Communication terminal 14 5 ACT connection terminal 15 Small CT connection terminal 16 Plug 31 Current detection unit 32 Voltage detection unit 33 Power calculation unit 311, 311 a, 311 b Load resistance 312, 322 Filter 313, 323 Adder circuit 331, 332 A / D conversion unit 333 Multiply unit 334 Transmission circuit section 335 Signal detection section 336 Control circuit section

Claims (16)

A voltage detector that detects a voltage signal from the circuit, a current detector that detects a current signal based on an output from a current transformer attached to the circuit, and the voltage detector and the current detector. A power calculator comprising: a power calculator that calculates power based on each voltage and current signal;
The current detection unit includes a signal processing circuit in which at least two types of burden resistors are connected in series, and the voltage of the burden resistors connected in series is signal-processed.
The current transformer is composed of at least two kinds of different outputs,
These current transformers are connected to a predetermined position of the load resistor connected in series or another predetermined position different from the predetermined position according to the type of the current transformer. A relay for conduction is connected in parallel to at least one burden resistor among the burden resistors connected in series,
The power measuring device according to claim 1, wherein the current transformer is connected to both ends of the burden resistor connected in series. The current detector is
A common connection terminal connected to a predetermined position at the end of the load resistor to which a signal line serving as a reference for the output of the current transformer is connected, and connected to a predetermined position at the end of the load resistor and connected to the predetermined position. Individual connection terminals to which the other signal lines of the flutes are connected;
The power meter according to claim 1, further comprising: a multiplexer having a circuit switching function for selecting a path of a signal line connected to the power calculation unit from the individual connection terminal. The power calculation unit includes a signal detection unit that detects a magnitude of a current signal input from the current detection unit,
The power measuring device according to claim 2, wherein the signal detection unit switches the setting of the relay or the multiplexer to another circuit based on the magnitude of the signal of the current.   5. The power measuring instrument according to claim 1, wherein the order of connecting the plurality of burden resistors in series lowers the resistance value of the burden resistor on the reference potential side.   6. The power measuring instrument according to claim 1, wherein a signal line on a reference potential side connected to the burden resistor is connected to a predetermined reference potential other than 0 V that is a ground. 6. .   The power measuring device according to any one of claims 1 to 6, wherein the current detection unit further includes a programmable gain amplifier capable of changing a signal amplification factor.   8. The connection terminal provided between the load resistors is not shared by the different types of current transformers, and is provided individually for each type of current transformer. The power meter described in 1.   The connection terminal connected to the load resistor having a larger resistance value among the at least two types of load resistors connected in series has a structure in which only a dedicated terminal can be connected. Item 9. The power measuring instrument according to Item 8.   The power measuring device according to claim 9, wherein the signal line from the current transformer is connected to a connector terminal having a shape that fits with the connection terminal.   The power measuring instrument according to claim 10, wherein the connector terminal has a structure to which at least two or more signal lines from the current transformer can be connected. The circuit includes a main circuit and a plurality of branch circuits branched from the main circuit,
The power measuring device according to any one of claims 3 to 11, wherein the connection terminal is arranged on a side surface of the power measuring device adjacent to each other for each of the circuits. The connection terminal includes a screw terminal for connecting a signal line of the current transformer with a large output, and a connector terminal for connecting a signal line of the current transformer with a small output;
The plug connected to the signal line of the current transformer has a structure that covers the other connection terminal when connected to one of the screw terminal or the connector terminal. Power meter.   The power measuring device according to any one of claims 1 to 13, wherein the power measuring device is capable of measuring power of a multi-circuit.   The power measuring device according to claim 14, wherein the connection terminal includes only the screw terminal or only the connector terminal for a part of the multi-circuit. A voltage detector that detects a voltage signal from the circuit, a current detector that detects a current signal based on an output from a current transformer attached to the circuit, and the voltage detector and the current detector. A power calculator comprising: a power calculator that calculates power based on each voltage and current signal;
The current detection unit is connected to at least two kinds of burden resistors arranged in parallel and one end side of the burden resistors arranged in parallel, and the current path of the output of the current transformer is connected in parallel. A circuit switch for switching to any path of the burden resistance, and a control circuit unit for controlling the circuit switch based on the magnitude of the current detected by the current detection unit,
The current transformer is composed of at least two kinds of different outputs,
These current transformers are connected to both ends of the burden resistor connected in parallel, and the power measuring instrument.

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